1. Field of the Invention
The present invention relates to a negative type resist composition for a color filter, which has excellent pigment dispersibility and alkaline developability.
2. Description of the Related Art
With development in personal computers, particularly with development in portable personal computers, demands for liquid crystal displays have recently been increasing. In addition, the penetration rate of household liquid crystal televisions has been also recently rising, so that the market of the liquid crystal displays has been expanding. Further, the screens of the liquid crystal displays having spread in these days tend to become larger. Particularly, as to the household liquid crystal televisions, this tendency is getting stronger. Under the circumstances, it is desired that high quality parts for the liquid crystal displays are produced at a lower cost with high productivity. Such a desire is increasing, because color filters having a function to perform color-displaying of liquid crystal displays have been high-cost item.
Here, as a general method for producing an color filter, a method is used, wherein a coated film made of a photo curable resist composition having each color pigment dispersed therein is formed on a substrate where a light-shielding portion is formed in pattern, and a color layer for each color is formed in pattern by subjecting the substrate to exposure and alkaline development via a photo mask having a desired pattern shape.
As the photo curable resist composition to be used for producing such a color filter, a composition comprising a pigment dispersant to be added for uniformly dispersing the pigment, an alkaline-soluble resin, a polyfunctional monomer, a photo initiator and a solvent in addition to the above mentioned pigment for each color is usually employed. As the pigment dispersant to be used in such a photo curable resist composition, a dispersant exhibiting excellent dispersibility is used, because if the dispersibility of the pigment in obtaining the color layer for the color filter is insufficient, problems such as color unevenness may occur in the color layer. As the photo curable resist composition using the pigment dispersant with such excellent dispersibility, a color filter composition using an A-B block copolymer and/or a B-A-B block copolymer, in which an A block has a quaternary ammonium base at side chains and a B block has no such a quaternary ammonium base at side chains as the pigment dispersant, is disclosed as a pigment dispersant (Japanese Patent Application Publication (JP-A) 2002-31713).
Further, a demand for enhancing the contrast ratio of the liquid crystal display apparatuses has been recently increasing, and the pigments are required to be made finer so as to realize such a demand. Owing to this, the surface area of the pigment in the above photo curable resist composition becomes bigger, and that addition amount of the pigment dispersant which is required to uniformly disperse the pigment needs to be increased.
However, as to the conventional type pigment dispersant containing the quaternary ammonium base as disclosed in JP-A 2002-31713, the uniform dispersibility of the pigment can be ensured by increasing the addition amount thereof. On the other hand, there are problems that the alkaline developability decreases, the time period required for the alkaline development becomes longer and the non-exposed photo curing resist composition remains on the substrate, the productivity and quality unfavorably drop.